1. Field of the Invention
This invention relates to rubbery copolymers of isoolefins.
More specifically, the invention relates to ozone resistant copolymers of isoolefins with certain non-conjugated diolefins and methods for preparing them.
2. Prior Art
Copolymers comprising a major portion of an isoolefin and a minor portion of a conjugated multiolefins are referred to in the patents and literature as "butyl rubber"; see, for example, the textbook Synthetic Rubber by G. S. Whitby (1954 edition by John Wiley & Sons, Inc.), pages 838-891, and "Isobutylene Polymers", Encyclopedia of Polymer Science and Engineering (Vol. 8, 2nd Ed., 1987, John Wiley & Sons, Inc.) pages 423-448. The preferred isoolefin is isobutylene. Suitable conjugated multiolefins include isoprene, butadiene, dimethyl butadiene, piperylene, etc., especially, isoprene
Commercial butyl rubber is a copolymer of isobutylene and minor amounts of isoprene. It is generally prepared in a slurry process using methyl chloride as a diluent and a Friedel-Crafts catalyst, typically AlCl.sub.3, as the polymerization initiator. The methyl chloride offers the advantage that AlCl.sub.3, a relatively inexpensive Friedel-Crafts catalyst, is soluble in it, as are the isobutylene and isoprene comonomers. Additionally, the butyl rubber polymer is insoluble in the methyl chloride and precipitates out of solution as fine particles to form a slurry. The polymerization is generally carried out at temperatures of about -90.degree. C. to -100.degree. C. See U.S. Pat. Nos. 2,356,128 and 2,356,129 incorporated herein by reference.
Conventional high molecular weight butyl rubber generally has a number average molecular weight of about 25,000 to about 500,000, preferably about 80,000 to about out 300,000, especially about 100,000 to about 250,000. Low molecular weight polymers have also been prepared with number average molecular weights of from 5,000 to 25,000. Polymers of even lower number average molecular weight, e.g. 500-5,000, can be produced if desired.
U.S. Pat. No. 2,384,975 to Sparks et al discloses copolymers of isolefins with polyolefins broadly represented by the formula ##STR3## where R is an alkyl group, n is a whole number greater than 2 and x is an uneven number. This formula encompasses an enormous number of possible compounds. Many of these will not work in the copolymerization process; some because they will result in a gelled polymer; others because they are inert (when R is, for example, t-butyl or isopropyl, the resulting diolefine will not polymerize). Furthermore, although the patent refers to nonconjugated diolefins, the general formula is not so restricted (e.g. when n=5 and x=3). There is no recognition in the patent of the advantage in ozone resistance to be achieved by using the dienes of the present invention or the other benefits obtained thereby, including high copolymerization activity without gel formation and high vulcanization activity.
United Kingdom Pat. No. 1,059,580 to Polymer Corporation Limited discloses essentially soluble, vulcanizable copolymers of a C.sub.4 to C.sub.7 isolefin (55-99.7 mol %) with a non-conjugated diolefin of the general structure ##STR4## wherein R is an alkyl hydrocarbon radical having 1-3 carbon atoms or a phenyl radical, Z is a methylene or paraxylylene radical, n is from 1 to 4 when Z is methylene and n=1 when Z is paraxylylene, and Y is hydrogen or methyl. The polymerization is carried out by dispersing the monomers in a non-reactive diluent such as an alkyl halide, cooling the mixture to between 0.degree. C. and -164.degree. C., and adding a Friedel-Crafts catalyst while stirring.
U.S. Pat. No. 4,551,503 to Lal et al. discloses co-polymers of alpha-olefins and non-conjugated alpha, omega-dienes prepared by the use of organoaluminum compound-transition metal compound catalysts modified with hexa (hydrocarbyl) phosphoric triamides or organophosphate esters.
European patent application No. 48,627 to Marsh discloses a process for preparing low molecular weight liquid polymers of 1-olefins, including co-polymers with non-conjugated dienes including vinyl norbornene, d-limonene and 2-methyl-1,5-hexadiene, involving the use of a catalyst system comprising an organo-aluminum compound, a methylallyl halide (which may also serve as a monomer), and a halide of tin or titanium.
European patent application No. 111,391 to Polysar Limited discloses tripolymers of isobutylene, isoprene, and 2,5-dimethyl 1,5-hexadiene, among others.